This invention relates generally to mine ventilation structures and more particularly to a mine ventilation structure used at the intersection of two mine passageways to prevent mixture of ventilation air in the two passageways.
A mine ventilation structure of the type to which the present invention generally relates can be either an "overcast" or an "undercast" mine ventilation structure. Overcast and undercast mine ventilation structures are widely used in underground mining to prevent the mixture of forced (or induced) ventilation air flowing through a first mine passageway with forced (or induced) ventilation air flowing through a second mine passageway at the intersection of those passageways. An overcast ventilation structure is a tunnel erected in the first passageway and extending through its intersection with the second passageway. The tunnel blocks communication of air between the first passageway and the second passageway at the intersection, but permits air in the second passageway to travel through the intersection in a passage created by a space between the roof of the tunnel and the mine passageway ceiling. An undercast is of similar construction, except that the air in the second passageway passes under the erected tunnel in a slot cut in the floor of the mine passageways at the intersection.
Mine ventilation structures are presently constructed in several different ways. A commonly used overcast ventilation structure includes side walls made of concrete blocks. Rails or I-beams bridging between the side walls at locations spaced longitudinally of the side walls form the superstructure for the roof of the overcast. The spaces between the rails or beams are filled in with, typically, corrugated steel panels or flat concrete blocks so that the a deck may be formed on the roof superstructure. Overcast ventilation structures may also be formed from tunnel liners, that is, structures which were intended to support the walls of the mine passageway. Tunnel liners are usually steel arches with heavy wood lagging, or steel plates that can be pinned or bolted together to form an archway to form the overcast tunnel. The use of a tunnel liner as a ventilation structure departs from its intended use. Both types of overcast structures described require several persons and large quantities of material to construct.
Another type of mine ventilation structure to which the present invention particularly relates has side walls formed from telescoping steel panels of the kind used for mine stopping described in co-assigned U.S. Pat. No. 4,483,642, which is incorporated herein by reference. A deck of the tunnel (constituting either the roof or the floor of the tunnel) is formed by relatively large, flat rectangular steel panels extending between the side walls. In an overcast ventilation structure, the panels are supported at the top of the side walls, while in an undercast ventilation structure, the panels are supported on either side of a slot cut in the mine floor. However, the panels cannot support their own weight and substantial loads over the span between the side walls or sides of the slot, and it is necessary that they be suspended by wires from the roof of the mine passageway. The installation of the wire supports requires skill on the part of the installers and consumes a significant portion of the total time taken to construct the ventilation structure. In addition, the wires may become loose if the mine walls shift and converge. When the ventilation structure is an undercast, the wires obstruct the path of travel through the tunnel, particularly machinery passing through the tunnel.